Terpolymers of acrylamide, alkylacrylamide and betaine monomers

ABSTRACT

A water soluble terpolymer having the structure: ##STR1## wherein x is selected from the group consisting of ##STR2## wherein x is about 1 to about 95 mole percent; y is about 0.1 to about 5.0 mole percent; R 1  is methyl or hydrogen; z is about 1 to about 30 mole percent; R 2  is an alkyl group of 1-5 carbon atoms; R 3  is an alkyl group of 3 to 4 carbon atoms; R 4  is an alkyl group of 1-5 carbon atoms; and R 5  is an alkyl group of 4-20.

This is a continuation of application Ser. No. 814,252, filed Dec. 30,1985, now U.S. Pat. No. 4,650,848.

BACKGROUND OF THE INVENTION

Poly(sodium acrylamidomethyl propane sulfonate), polyacrylamide andpartially hydrolyzed polyacrylamide, and copolymers thereof are watersoluble polymers that have been previously disclosed in the literatureand have found application in the viscosification of aqueous solutions.These polymers viscosify through a combination of high molecular weightand chain expansion due to repulsion of pendant ionic groups along thepolymer chain or H-bonding. These polymers are salt-sensitive, therebylimiting their application in highly saline systems.

The betaines are a special class of zwitterions. These materials areself neutralized and contain no counterions. Moreover, the positive andnegative charges are separated by alkyl groups.

Carboxymethacrylate betaine monomers (I) and polymers (II) arewell-known and disclosed in U.S. Pat. No. 2,777,872 (Jan. 15, 1957),U.S. Pat. No. 2,834,758 (May 13, 1958) and U.S. Pat. No. 2,846,417 (Aug.5, 1958). ##STR3##

Carboxyvinylpyridine betaine monomers and homopolymers (III) have alsobeen reported [H. Ladenheim and H. Morawetz, J. Poly. Sci. 26, 251(1957)]. ##STR4##

Sulfovinylpyridine betaine monomers and homopolymers (IV) are known [R.Hart and D. Timmerman, J. Poly. Sci. 28, 118 (1958)] and Ger.Auslegeschrift No. 1,207,630 and Galin, et al., Polymer, 25, 121,254(1984). ##STR5##

The butylsulfobetaine of poly(2-vinylpyridine) (IVB) is soluble inwater, but the butylsulfobetaine of poly(4-vinylpyridine) (IVA) is not.Both betaines are soluble in salt solution.

Methacrylate based sulfobetaine monomers and homopolymers (V) aredescribed by Galin Polymer, 25, 121,254 (1984) and Ger. AuslegeshriftNo. 1,207,630, U.S. Pat. No. 3,549,605 and U.S. Pat. No. 3,493,547.##STR6##

Copolymers of acrylamide and methacrylate and vinyl pyridine betainemonomers, like IV and V, are described in Ger. Auslegeschrift No.1,207,630.

In turn, copolymers of long chain alkyl acrylamide and acrylamide havebeen described by Bock, et al. (U.S. Pat. No. 4,520,182). Enhancedviscosification is claimed for the latter materials. Such materials areprepared by special micellar (U.S. Pat. No. 4,528,348) or microemulsion(U.S. Pat. No. 4,521,580) polymerization methods using surfactants likesodium lauryl sulfate (SDS) to incorporate the long chainalkylacrylamide

SUMMARY OF THE INVENTION

The present invention relates to unique and novel betaine terpolymerswhich are terpolymers of acrylamide, long chain N-alkylacrylamide andester-, amide- or vinyl pyridine-based betaine monomers. Such polymerscontain both zwitterion and hydrophobic groups and are represented bythe following structures: ##STR7## wherein x is about 70 to about 95mole percent, more preferably about 80 to about 90 mole percent; y isabout 0.1 to about 5.0 mole percent, more preferably about 0.2 to about3.0; and z is about 1 to about 30 mole percent, and more preferablyabout 5 to about 20 mole percent. R₁ is methyl or hydrogen; R₂ is analkyl group of 1-5 carbons; R₃ is an alkyl group of 3-4 carbons, R₄ isan alkyl group of 1-5 carbon atoms; and R₅ is an alkyl group havingabout 4-30 carbon atoms, more preferably about 5 to about 20 carbonatoms.

Thus, the instant structures are different from conventionalpolyelectrolyte homo- or copolymers, which contain either positive ornegative charges. In addition, unlike conventional polyelectrolytes, theaqueous viscosities of the instant materials increase with increasingconcentration of salts, like sodium chloride.

The present invention is distinguished from the carboxymethacrylatebetaine homopolymers and copolyers (U.S. Pat. Nos. 2,777,872, 2,834,758,2,846,417) due to the presence of sulfonates rather than carboxylateanions and low in contrast to high charge densities are used.Furthermore, carboxylate anions are limited by their known susceptiblityto precipitation by polyvalent cations (e.g. Ca⁺⁺); the latter speciesare often found in geological formations [F. J. Glaris in "Water SolubleResins" 2nd Ed, R. L. Davidson and M. Sittig, Eds. Rheinhold, NY, p.168]. Sulfonate anions are not so limited.

The instant invention is different from other sulfobetaine polymers ofthe art by virtue of the presence of the hydrophobic group(N-alkylacrylamide), by the mode of preparation (i.e., micellar ormicroemulsion polymerization with sodium lauryl sulfate, SDS) and by thesurprisingly high enhancement in viscosities with increasing saltcontents.

The instant terpolymers are distinguished from the copolymers ofacrylamide and long chain N-alkyl acrylamides by their chemicalstructures and their unexpected high retention of viscosity in highconcentrations of brine (e.g., NaCl).

GENERAL DESCRIPTION OF THE INVENTION

The present invention relates to a method for increasing the viscosityof a salt solution which comprises the step of dissolving about 0.1 toabout 5.0 wt.% of a water soluble terpolymer ofacrylamide/N-alkylacrylamide/betaine in an aqueous solution, wherein theaqueous solution is selected from the group consisting of water or abrine solution and the concentration of the brine in the aqueoussolution is about 0.01 to about 20.0 wt.%.

The viscosifying agents for aqueous and saline solutions of the presentinvention are betaine terpolymers formed by a homogeneous, free radical,terpolymerization, wherein the water soluble terpolymers arecharacterized by the formulae: ##STR8## wherein x is about 70 to about95 mole percent, more preferably about 80 to about 90 mole percent; y isabout 0.1 to about 5.0 mole percent, more preferably about 0.2 to about3.0; and z is about 1 to about 30 mole percent, and more preferablyabout 5 to about 20 mole percent. R₁ is methyl or hydrogen; R₂ is analkyl group of 1-5 carbons; R₃ is an alkyl group of 3-4 carbons, R₄ isan alkyl group of 1-5 carbon atoms; and R₅ is an alkyl group havingabout 4-30 carbon atoms, more preferably about 5 to about 20 carbonatoms.

The viscosities of aqueous solutions of these betaine terpolymers weremeasured by means of a Contraves™ low shear viscometer model LS30 usinga No. 1 cup and No. 1 bob. Temperatures were controlled to ±1° C., andmeasurements were made at a rotational speed that gave a shear rate of1.28 s⁻¹.

The homogeneous terpolymerization process of the instant inventioncomprises the steps of forming a mixture of acrylamide monomer, longchain N-alkylacrylamide monomer and betaine monomer in the presence ofSDS surfactant under a nitrogen atmosphere; adding deoxygenated water tosaid mixture to form a reaction solution; adding a free radicalinitiator to said reaction solution to initiate the copolymerization ofthe acrylamide monomer, long chain N-alkylacrylamide monomer and thebetaine monomer; polymerizing the monomers at a sufficient temperatureand for a sufficient time to form the water soluble ter polymer ofacrylamide monomer, N-alkylacrylamide monomer and betaine monomer; andrecovering the water soluble terpolymer from the reaction solution. TheSDS is present in the polymerization to facilitate incorporation of thealkylacrylamide, as in U.S. Pat. No. 4,521,580 and U.S. Pat. No.4,528,348.

Suitable free radical initiators for the instant freeradical-copolymerization process are potassium persulfate; sodiumthiosulfate, potassium persulfate mixture; benzoyl peroxide, AIBN andother common free radical initiators. The concentration of the freeradical initiator is about 0.02 to about 0.50 grams per 100 grams oftotal monomer.

Polymerization of the acrylamide monomer, N-alkyl acrylamide monomer andN-3(3-sulfopropyl)-N-methacryol-oxyethyl-N,N-dimethyl-ammoniumbetaine(SPE) monomer is effective at a temperature of about 25° to about 90°C., more preferably at about 30° to about 65° C., and most preferably atabout 45° to about 55° C. for a period of about 1 to about 48 hours,more preferably at about 2 to about 36, and most preferably at about 4to about 24. A suitable method for recovery of the formed terpolymerfrom the reaction solution comprises precipitation by means of acetone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following examples illustrate the present invention without,however, limiting the same hereto.

EXAMPLE 1 (9722-124) Terpolymer of Acrylamide, Alkylacrylamide, andN-(3-Sulfopropyl)N-Methacroyloxethyl N,N-dimethyl Ammonium Betaine(SPE), RAM/SPE, AM/C₈ AM/SPE=94/1/5 Mole %

A 1,000 ml resin flask was fitted with a condenser, electric stirrer,thermometer, N₂ inlet and outlet. The flask was purged with N₂ for 1hour while water was boiled and cooled under N₂. To the flask wascharged 470 grams of H₂ O, 12.13 grams recrystallized acrylamide, 0.33grams n-octylacrylamide, 15.85 grams SDS (sodium dodecyl sulfate) and2.45 grams of SPE betaine monomer. The solution was heated to 50° C. andthe K₂ S₂ O₈ (0.01 grams) initiator was added. Polymerization wasevident after one hour. The run was continued for 24 hours at 50° C. Thesample was precipitated into acetone.

EXAMPLE 2 (9722-125) Copolymer of Acrylamide and Alkylacrylamide, RAM

A 1,000 ml resin flask was fitted with a condenser, electric stirrer,thermometer, N₂ inlet and outlet. The flask was purged with N₂ for onehour, while water was boiled and cooled under N₂. To the flask wascharged 470 grams of H₂ O, 14.62 grams recrystallized acrylamide, 0.38grams of n-octylacrylamide, 15.85 grams of SDS. The solution was heatedto 50° C. and 0.01 grams of K₂ S₂ O₈ initiator was added. The polymerwas precipitated in acetone and vacuum dried.

EXAMPLE 3 (9595-147) Copolymer of Acrylamide and SPE, AM/SPE

A two liter reaction kettle was equipped with an air driven stirrer,water condenser, thermometer and subsurface nitrogen purge. One liter ofdistilled deionized water was added and heated at 50°-55° C. for onehour while stirring and rapid nitrogen sweep. The nitrogen inlet wasraised and the monomers, acrylamide (30 grams), andN-(3-sulfopropyl)-N-methacryoloxyethyl-N,N-dimethylammonium betaine(SPE) (6.1 grams) were added. A 0.023 gram quantity of K₂ S₂ O₈initiator was charged and the polymerization continued at 52°-54° C. for19 hours. Polymer was isolated by acetone precipitation and vacuumdrying.

EXAMPLE 4 (9595-153) Copolymer of Acrylamide and Sodium StyreneSulfonated, AM/SSNa 95/5 Mole %

A control polyelectrolyte was prepared according to the method ofExample 3, except that sodium styrene sulfonate was substituted for SPE.Thus, 30 grams of acrylamide, 4.53 grams of poly (sodium styrenesulfonate) were charged to the reactor with one liter of distilled,deionized water. A 0.023 gram quantity of K₂ S₂ O₈ initiator was chargedand the polymerization continued for 51°-52° C. for 17 hours. The batchwas diluted with additional water, precipitated with acetone and vacuumdried.

EXAMPLE 5 Viscosities of Polymer Solutions With and Without Salt

Viscosities of polymer solutions with and without NaCl were measured ona Brookfield viscometer. The viscosity ratio (i.e., the viscosity of thepolymer solution in salt divided by the viscosity of the polymersolution in water) was used to indicate the effectiveness of polymers inmaintaining their viscosities in the presence of NaCl. Table 1 showsthat AM/SSNa, a classical polyelectrolyte, shows a viscosity ratio lessthan 1. In contrast, AM/SPE, RAM and RAM/SPE show viscosity ratiosgreater than 1. Furthermore, RAM/SPE shows a surprising synergisticincrease in viscosity ratio as one increases the salt concentration from2-20%.

                  TABLE I                                                         ______________________________________                                                Polymer                                                               Polymer Concentration          Viscosity Ratio                                Type    Wt. %         % NaCL   of Salt/NH.sub.2 O                             ______________________________________                                        RAM/SPE 0.5           0        --                                                                   2        6.5                                                                  5        11.0                                                                 10       170.0                                                                20       445.0                                          RAM     0.5           0        --                                                                   2        15.7                                                                 5        24.0                                                                 10       29.6                                                                 20       22.6                                           AM/SPE  1.8           0        --                                                                   2        1.2                                                                  5        --                                                                   10       1.6                                                                  20       1.5                                            AM/SSNa 1.7           0        --                                                                   2        0.4                                                                  5        0.3                                                                  10       0.3                                                                  20       0.3                                            ______________________________________                                    

What is claimed is:
 1. A water soluble terpolymer having the structure:##STR9## wherein x is selected from the group consisting of ##STR10##wherein x is about 70 to about 95 mole percent; y is about 0.1 to about5 mole percent; R₁ is methyl or hydrogen; z is about 30 mole percent; R₂is an alkyl group of 1-5 carbon atoms; R₃ is an alkyl group of 3 to 4carbon atoms; R₄ is an alkyl group of 1-5 carbon atoms; and R₅ is analkyl group of 4-20.
 2. A method for increasing the viscosity of anaqueous solution which comprises the step of dissolving in said aqueoussolution a water soluble terpolymer having the structure: ##STR11##wherein x is selected from the group consisting of ##STR12## wherein xis about 70 to about 95 mole percent; y is about 0.1 to about 5.0 molepercent; R₁ is methyl or hydrogen; z is about 1 to about 30 molepercent; R₂ is an alkyl group of 1-5 carbon atoms; R₃ is an alkyl groupof 3 to 4 carbon atoms; R₄ is an alkyl group of 1-5 carbon atoms; and R₅is an alkyl group of 4-20.